Semiconductor devices have currently been used widely in various fields. The semiconductor devices are usually used by mounting them on substrates. The mounting methods include bonding methods such as tape automated bonding (TAB), wire bonding and flip chip bonding.
The TAB and wire bonding are technologies by which a semiconductor device is mounted on a substrate through leads. The leads are arranged in one row per peripheral side of the semiconductor device. The technologies are, therefore, not suited to high density mounting of the semiconductor devices. In contrast to the technologies mentioned above, flip chip bonding is a technology by which the electrodes of a semiconductor device are directly connected to the electrode terminals on the substrate through a bonding metal. Since the electrodes of the semiconductor device can be provided in a lattice-like form on the entire surface, the technology is suited to high density mounting. Various solders are generally used as bonding metal in flip chip bonding because the bonding is conducted by melting at low temperature.
In flip chip bonding, semiconductor devices provided with low melting point metal bumps for bonding placed on electrodes are used, and the semiconductor devices are connected to the electrode terminals of substrates by a reflowing procedure by which the bumps are melted and solidified again.
In general, the bumps are formed by vapor deposition or plating. However, such bump formation methods must all repeat complicated treatments steps using a mask. Moreover, in the method of forming the bumps by vapor deposition, a bump material is deposited on portions where the bumps are not to be formed, and the deposition amount thereon is very large. The method is, therefore, not a preferred one in view of the cost and efficiency. Moreover, wet plating such as electroplating or electroless plating fouls wafers and causes an environmental problem, and countermeasures against such problems are indispensable. As illustrated above, conventional methods for forming the bumps are relatively costly, and practical use of the methods is restricted.
There is a stud bump procedure as a method for forming bumps other than vapor deposition and plating. Since bumps are formed one by one in the procedure, the production efficiency is low, and in addition the bump amount tends to vary among the bumps. Accordingly, securing uniformity in bonding the semiconductor devices and the substrates is difficult.